1. Field of the Invention
This invention relates generally to industrial and mobile hydraulic systems utilizing a variable volume (displacement) pump of the pressure and flow compensated (load sense) control type and, in one specific embodiment, to a valve or valve assembly configured to provide a soft or transitioned start or stop.
2. Technical Considerations
The utilization of variable volume pumps equipped and controlled by pressure and flow compensated (load sense) type valving in power transmission hydraulic systems is becoming more and more popular. This increased popularity is due, at least in part, to increased operational functionality, versatility and efficiency of hydraulic circuits and systems using this type of pump when compared to systems using various other pump types. The input power to drive these pumps is commonly supplied by an engine or motor of some type.
At times it may be desired to start or stop the fluid flow from the pump to the downstream components without stopping or disengaging the input power source from rotating the pump input shaft. Examples of such would be to shut off the pump flow supply to circuit components in the event of a fluid transmission line (hose) failure that may result in a fluid leak or spill or as a means to prevent undesired operation of system functions when the pump input power is being provided by a directly connected engine in a motor vehicle. Stopping the flow to these components by blocking or shutting off the flow from the pump outlet port can result in potentially harmful or dangerous hydraulic system operating characteristics, such as rapid and/or high pressure rises, commonly referred to as “spikes”. Spikes can occur in situations such as when the pump supply path is closed to flow while the system is at operational pressure or such as when the path closure rate is faster than the rate at which the pump displacement control system can respond. Spikes can also occur when the pump supply path is opened to flow when an operational pressure signal is present on the load sense control valve or when the valve flow path opening rate results in an excessive pump flow and pressure output due to pump displacement control system response lag. These characteristics can cause hydraulic system and pump powertrain component failure.
Therefore, it would be beneficial to provide a means of shutting off and/or turning on the flow from the pump outlet port in such a manner as to reduce or eliminate at least some of these undesired operational characteristics.